The present invention is directed to a black body background in the form of a light trap suitable for use in an optical imaging system.
Optical imaging systems are known in which an object, such as a sample which is being evaluated, is illuminated with electromagnetic radiation, and radiation reflected by the sample is detected by an imaging device such as a camera or an optical scanner, as shown in FIG. 1. The information gathered in this manner may be digitized and stored for processing in a digital computer. The reflected radiation may be detected in a plurality of spectral bands in a process known as multispectral or hyperspectral imaging. See, for example, U.S. Pat. No. 6,166,373 to Chengye Mao issued Dec. 26, 2000. Numerous such systems are known. By analyzing the spectral information gathered in this manner, it is possible to evaluate physical characteristics of the sample, as well as its composition.
An important consideration in such imaging systems is to assure that the radiation sampled by camera or optical scanner is limited exclusively to that which is reflected by the sample. For this purpose, it is conventional to place the sample in front of a non-reflecting surface, such as a flat black painted surface or a non-reflective black textile material. The idea is to prevent any light that has penetrated or gone around the sample from reflecting off the background and back into the camera or scanner. This allows for the capture of a more pure spectral signature from the sample.
Various arrangements have been proposed for reducing the amount of reflected radiation which emanates from the background surface in imaging and scanning systems such as described above. For example, U.S. Pat. No. 5,144,524 discloses the use of an antireflectance film to prevent scanning light from being scattered by particle contamination on a target surface. U.S. Pat. No. 5,745,293, on the other hand, discloses a light trap for use in optical systems and instruments, in which unwanted light is guided into a light trap in the form of an enclosure containing a conical body which is disposed in the light path. The light is attenuated by reflecting it in all directions from the conical body that facilitates its absorption by the internal walls of the enclosure.
U.S. Pat. No. 6,220,715 discloses a light trap that includes a spherical enclosure, with an opening for receiving a light beam. The interior of the enclosure has a light absorbing surface as well as a polished spheroidal reflector body that is disposed in the path of light that enters through the opening. The reflector disperses the incoming light within the sphere so that it can be absorbed.
The purpose of the present invention is to provide a light trap structure that is simple, inexpensive and easy to manufacture, and is suitable for use as a black body background in an imaging system such as described above.
Another object of the invention is to provide such a light trap structure that efficiently traps spurious radiation incident therein.
These and other objects and advantages are achieved by the light trap structure according to the invention, which includes a hollow sphere, with a hollow tube attached to one side in the form of a chimney. The sphere and chimney are coated (inside and out) with a low reflective coating, such as flat black paint, although any low reflectivity coating can be used. The sample to be imaged is placed on top of the chimney with the imaging system and lights above, aiming down into the chimney. Any light that passes through the sample is xe2x80x9ccapturedxe2x80x9d in the sphere section, so that it cannot reflect back to the imaging system.
The light trap according to the invention is extremely simple and effective. Initial tests have indicated a 75% reduction in reflected light, when compared to the same materials and coatings used in traditional setups (i.e., flat surfaces).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.